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Handout4 - Erin Yee [email protected] Handout 4 Pyruvate...

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Erin Yee [email protected] Handout 4 Pyruvate Dehydrogenase Complex (PDH Complex): Coenzymes: o E1: TPP (Thiamine Pyrophosphate) o E2: Coenzyme A (CoA) & Lipoyllysine o E3:: FAD & NAD_ E1 catalyzes two reactions: o Thiamine Pyrophosphate (TPP) reacts with Pyruvate through a decarboxylation reaction giving off a molecule of CO2 and forming the intermediate Hydroxyethyl TPP o The Hydroxyethyl TPP intermediate is then handed off to the Lipoyllysine arm on E2 forming an Acyl Lipoyllysine and reforming the original TPP E2 catalyzes two rxns: o Transferase rxn of handing off the Acyl group to CoenzymeA (CoA-SH) to form Acetyl-CoA o Allows the reduced Lipoyllysine arm to transfer the electrons on to E3’s FAD to form FADH2 E3 then transfers the electrons from FADH2 to NAD+ to form NADH
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In the end, we have a molecule of Acetyl-CoA and a molecule of NADH that can later enter the ETC PDH Regulation: Phosphorlyation of Enzyme 1 (Pyruvate Dehydrogenase) by Protein Kinase inhibits E1’s activity (turns it OFF). Protein Kinase is positively allosterically regulated by ATP. High concentrations of ATP turn Protein Kinase ON so that it can then turn OFF E1. Dephosphorylation of Enzyme 1 by Protein Phosphatase causes E1 to be ON. Protein Phosphatase is constitutively active or “on all the time” to make E1 active.
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